The present invention relates to a shock absorber which works with a bleed function. In this connection, the bleed function can interact with a non-return valve function. In certain embodiments, the shock absorber is preferably arranged so as to have both the bleed and the non-return valve functions. The shock absorber is also of the type which has a cylinder and, working in the latter in working medium and arranged on the piston rod, a piston arrangement which comprises at least two first and second pistons arranged at a distance from one another. At least one of said pistons can, in connection with an end position in the cylinder or the shock absorber, be introduced into a first space so as, depending on its position in or at the space, to bring about a modified or varied damping force compared with the case when the piston in question is located outside the space.
This type of shock absorber is previously known and reference can in this connection be made to inter alia U.S. Pat. No. 3,195,645. The present invention can be seen as a development in relation to this known shock absorber. The known shock absorber comprises a dual-piston arrangement in which the first or front piston enters and exits a cup-shaped container so as to bring about an increased damping force in the shock absorber end position concerned. A second piston of full-size diameter is made with fixed throttles via which the damping forces or damping capacity of the shock absorber can be implemented in positions outside said end positions. The known shock absorber also demonstrates that increased damping force can be obtained in both the end positions of the shock absorber.
Reference can also be made to UK Patent Specification 2 202 921 which indicates that, instead of a cup-shaped part which is arranged in the shock absorber end concerned, use can be made of a pin-shaped element which interacts with a recess in the piston rod end and in this way acts on an arrangement which increases the damping force via the shock absorber end concerned.
Reference can also be made very generally to European Patent Specification 565 832 B1.
It is also known per se to arrange for a bleed function in a shock absorber. What is known as return bleed is used in order to make the wheels of the vehicle follow the surface of the ground better. By arranging a bleed flow past a member which is arranged on the piston in question and acts on the medium, forward, upward and return (downward) movements are made easier. The use of a non-return valve in the return bleed makes possible separation of compression bleed and return bleed to different degrees, which can be selected depending on the non-return valve selected.
It is desirable to be able, in accordance with said U.S. Patent Specification, to arrange a dual-piston arrangement of the type disclosed also on those types of shock absorber which have on the one hand a cylinder for a piston rod and a dual-piston arrangement in working medium essentially in the form of hydraulic oil, and on the other hand a container for an accumulator function, which is connected to the cylinder via an intermediate part, a hose or a pipe connection etc. In this respect, it is essential to be able to arrange an appropriate bleed function, if appropriate together with a non-return valve function, in the structure so that an integrated construction which functions well is obtained. The invention aims to solve this problem inter alia.
In the use of a bleed or non-return valve function, it is often advantageous to be able to arrange the member performing the bleed function so that regulatability or adjustability can be achieved. It is to be possible to implement this adjustability by means of members known per se in a manner known per se. The invention solves this problem also.
As claimed in the present invention, it is also desirable that dual-piston and bleed and non-return valve arrangements can work with a piston function provided with shims, by means of which a speed-dependent damping force function can be achieved. The invention solves this problem also.
In connection with said UK Patent Specification, the arrangement of a conical pin-shaped element involves a problem associated with being able to use the interior of the piston rod for mounting and positioning members which can effect said bleed and/or non-return valve functions. The invention solves this problem also and indicates a basic structure with a cup-shaped element as claimed in said U.S. Patent Specification or a corresponding arrangement.
In connection with the device or shock absorber as claimed in said UK Patent Specification, there is also a problem associated with being able to clearly and unambiguously separate the functions of the first and second pistons. As claimed in the invention, the first piston is to be capable of effecting its end damping force function without being influenced by the second piston. The invention solves this problem also by proposing a basic concept based on the U.S. Patent Specification.
As claimed in the invention, seat and nozzle functions are to be arranged for effecting said bleed function. The invention solves this problem also and proposes in this connection a unique arrangement for a piston rod, construction and arrangement of the second piston with its associated shims and also construction and arrangement of the first piston on the piston rod.
There is also a requirement to be able to use alternative constructions and functions in connection with the bleed function in a shock absorber of said type with a dual-piston arrangement and shims arranged on the latter. The invention solves this problem also and proposes an alternative or additional arrangement in which the bleed function is separated from or integrated with the non-return valve function.
A shock absorber of the type described in the introduction can be considered to be mainly wherein either the piston rod is provided with an inner second space which is arranged so as to accommodate said bleed function and any non-return valve function arranged with the latter, or the second piston is made with a bleed function and any non-return valve function interacting with the latter.
In developments of the inventive idea, it is proposed that said first space is to be arranged in a cup-shaped or sleeve-shaped part which is located in said end position in question in the cylinder or the shock absorber. In this connection, a cup-shaped or sleeve-shaped part can be located in each end position in the cylinder. The first cup-shaped part can then serve the first piston in the first end position, and the second cup-shaped part can serve a third piston in the second end position. Said first and/or third piston can then have a sleeve-shaped part which, in the end position in question, is involved in forming said first space in the end position concerned. An alternative to forming the first space with a cup-shaped part is to make the cylinder wall with a thickened wall in the portion concerned.
In further embodiments, both a member performing the bleed function and a member performing the non-return valve function are arranged in the second space. In this connection, the member performing the bleed function can be arranged so that it can be controlled in order to obtain a bleed function which can be regulated by controls. The second space can also consist of a recess extending in the longitudinal direction of the piston rod, at the first end of which the member performing the bleed function is arranged and in which an operating rod extending in the recess, toward the second end of the recess, is arranged. At said second end, the operating rod can be acted on by means of a wheel or equivalent adjusting member. The member performing the non-return valve function is located outside the member performing the bleed function, that is to say closer to the free end of the piston rod in a case where the outer piston of the piston arrangement or the first piston can be introduced into the cup-shaped or sleeve-shaped part. The latter part can be arranged with a side gap or side hole which preferably extends in the longitudinal direction of the cylinder and via which the cylinder space in front of the second piston can be connected by one or more ducts to an accumulator container arranged separately in relation to the cylinder. The second space or recess can also be connected, via one or more first passages or side holes in the piston rod wall, to the space outside the outer wall of the piston rod between the first and second pistons. The second space can also be connected, via one or more second passages or side holes in the piston rod wall, to the space outside the piston rod behind the second and, respectively, in front of the third piston. When an expansion movement takes place, the bleed function is activated by virtue of the fact that working medium can pass from the upper side of the second piston, to each second passage or side hole, onward via the member performing the bleed function, to each first passage or side hole, and out at the front side of the second piston. When a compression movement takes place, the member performing the non-return valve function prevents the working medium flowing via the member performing the bleed function. Alternatively, the non-return valve arrangement can act on the passage for the working medium relative to when an expansion movement takes place, it being possible to make the passage smaller or larger.
In other developments of the inventive idea, the first or front piston, that is to say the piston closest to the free end of the piston rod, has a diameter which corresponds to the diameter of the first space and is smaller than the diameter of the rest of the cylinder part. The first piston is also made with first working medium passages which are used essentially in the position of the first piston in the first space. The working medium flows via the working medium passages when the first piston is working in the cup-shaped or sleeve-shaped part. The second piston has on the one hand a diameter corresponding to the full-size diameter of the cylinder, and on the other hand second working medium openings, at which shims or shim packs are arranged on the lower and upper sides of the second piston. A continuous damping-force regulation function is therefore afforded by means of the shims or shim packs of the second piston, and increased end position damping is effected by means of the position of the first piston in or at the first space. The shock absorber can be intended for use on a motorcycle or a two-wheeled or three-wheeled vehicle. The shock absorber can also be used to form part of a car or a four-wheeled vehicle.
In one embodiment, the piston rod consists of a first piston rod part which, at the front, is made with a part of reduced diameter, on which the second piston is mounted. The piston rod can also comprise a second piston rod part of bushing-like design, in which the part of reduced diameter extends. Furthermore, the shims or shim packs of the second piston on the upper and lower sides of the second piston can be secured by means of a disc-shaped element positioned between a transition at the part of reduced diameter and the shim or the shim pack on the upper side of the piston. An end surface on the second piston rod part can bear against the shim or shim pack on the lower side of the second piston. The second piston rod part bears the first piston on a spindle-shaped portion of reduced diameter, at the end of which a securing member is arranged, for example a nut (lock nut), so as to press together in the axial direction and hold together the piston rod parts and the first and second pistons and also the shims/shim packs of the second piston and said disc-shaped element. In a preferred embodiment, the first and second piston rod parts form portions of the second space. In that portion of the second space formed by the first piston rod part, a nozzle with a seat is positioned, which forms said member performing the bleed. In this connection, the first and second passages or side holes as claimed in the above can be located on each side of the nozzle. In one embodiment, use is made of a non-return valve which can be acted on by medium pressure on compression and when it is acted on closes a passage for the bleed flow. The non-return valve can have a bleed hole for said flow. The bleed flow passes via the bleed hole when the valve has closed said passage. In this way, different rates of bleed flow can be obtained on expansion and compression. When there is no bleed hole in the non-return valve, the bleed flow is prevented completely. In a further embodiment, the bleed member and any non-return valve member are positioned in the second piston by way of an additional or alternative arrangement.
By means of the above, an advantageous construction of the shock absorber as such from an economic point of view is obtained. The new functions can be built into a shock absorber which can be of a type known per se, for example of the xc3x96hlins Racing AB type of shock absorber designated 46PRC, 46HR, 46R etc. The bleed and/or non-return valve function can be adapted optimally to other functions in the shock absorber. The shock absorber can thus be provided with a bleed function and a non-return valve function which function as claimed in the requirements of the customer. The new functions can be built into modern shock absorbers such as those of said type. In this connection, it is essential that shock absorbers with accumulators can be provided with the new functions. For example, it is to be possible for the bleed function to be present when an expansion movement takes place in the end position concerned, while it is prevented or acted on/modified when compression movement takes place in said end position. When a non-return valve is used, this can be arranged to have a bleed hole for the bleed flow or can be without such a bleed hole, that is to say the bleed function is prevented on compression. Alternatively, non-return valves with bleed holes of different size for acting on the bleed flow to varying degrees on compression can be arranged. A non-return valve with a suitable bleed hole or without a bleed hole is selected by testing. The selection depends on the travelling position the driver wants for the vehicle. In the curve chart in question, the bleed range is up to 0.4 m/s with variations upward and downward in the speed range, depending on which shim pack and bleed needle size are used. The selection depends on the situation, the driver and the vehicle. On the shock absorbers available from xc3x96hlins Racing AB, 3.2 and respectively 4.0 mm return bleed needles are used with nozzles. Quite generally, use is made of a larger needle/nozzle and vice versa. With the bleed function, the damping force is reduced around the zero range.